Fear and Fright

August 12, 1877: Deimos is discovered. The smaller moon of Mars was located by Asaph Hall who went on, five days later to find Phobos as well. Deimos is 9.3 x 7.6 x 6.8 miles while Phobos is 16.8 x 13.7 x 11.2 miles. Both moons are non-spherical and resemble C- or D-type asteroids. It is theorized that both were once asteroids which had orbits disturbed by Jupiter and were thrown out of their paths and then captured by Mars. Both moons also have very circular orbits almost exactly in line with Mars’s equatorial plane. This means some process must have been used to shift their orbits once they were captured by the planet. Deimos has an orbit about 14,477 miles from Mars and takes 30.312 hours to orbit the planet. Phobos is only about 5,825 miles away and rapidly circles Mars every 7 hours and 39 minutes.

Hall was working at the US Naval Observatory in Washington, D.C. He had seen what he thought was perhaps a Martian moon on August 10 but bad weather kept him from certainty. The telescope he was using was a 26-inch refractor. The telescope had a lens remounted in 1893 and put in a new dome where it remains to this day. The two moons were named after a suggestion by Henry Madan, Science Master of Eton. The names refer to the twins in Greek mythology who personified Terror as Fear and Fright. Deimos has two geological features that have been named. There are two craters, one named Swift after Jonathan Swift and the other named Voltaire. Voltaire’s diameter is nearly twice that of Swift’s.

Asaph Hall III was born in 1829 in Goshen, Connecticut. His father was a clockmaker. His grandfather was a Revolutionary War officer as well as a Connecticut state legislator. The Hall family was put in financial difficulties when his father died in 1842. Hall quit school at 16 to become a carpenter’s apprentice. He was later able to study mathematics at Central College and then married one of his instructors, Angeline Stickney. They married in 1856, the same year Hall took a job at the Harvard College Observatory in Cambridge, Massachusetts. His forte was computing the orbits of heavenly bodies. He became an assistant astronomer at the US Naval Observatory in 1862. By the next year, he was made a professor.

He was given responsibility for the telescope in 1875. At the time, it was the largest refractory telescope in the world. Two years later, he made this auspicious discovery. He also noticed a white spot on Saturn which he used to calculate the planet’s rotational period. He wrote a paper describing one of the earliest documentations of random sampling. He retired from the Navy in 1891 and became a lecturer at Harvard where he remained until 1901. Hall had four children, all of whom were highly accomplished, one of them following in his footsteps and taking up astronomy. Hall died in 1907 at the age of 78.

Beauty is the first test: there is no permanent place in the world for ugly mathematics. – G. H. Hardy

I am acutely aware of the fact that the marriage between mathematics and physics, which was so enormously fruitful in past centuries, has recently ended in divorce. – Freeman Dyson

In mathematics, as in physics, so much depends on chance, on a propitious moment. – Stanislaw Ulam

Also on this day: NAFTA – In 1992, NAFTA negotiations concluded.Personal Computer – In 1981, IBM released a new personal computer.Model T – In 1908, the first Model T was produced.Boon for Butterick – In 1851, Isaac Singer received a patent for a sewing machine.Cleopatra – In 30 BC, the Egyptian leader died.